1. Field of the Invention
The invention relates to a retaining device for a heat sink and to the retaining and positioning technology for a central processing unit and the heat sink applied to the heat dissipating field of a digital data processing device, and more particularly to a retaining device for a heat sink capable of simplifying a positioning device of the invention and ensuring the good retaining effect.
2. Description of the Related Art
A central processing unit (CPU) is a heart for a digital processing device. The CPU generates heat as it is operating. In order to dissipate the heat of the CPU and thus to prevent the heat from influencing the operating efficiency of the CPU, a retaining device is provided to fix a fin-like heat sink to the CPU. As shown in FIG. 8, the retaining device includes a retaining arm 75, a retaining piece 80, a combination seat 85 and a switch element 90. The retaining arm 75 has one end formed with a retaining hole 76 and the other end, into which the retaining piece 80 may be inserted vertically. The bottom end of the retaining piece 80 is also formed with a retaining hole 81. The retaining piece 80 penetrates through the top end of the retaining arm 75 and then inserted into and positioned at the combination seat 85. The combination seat 85 is disposed in the hollow switch element 90, which has two guiding bevels 91 and 911 with different heights and arced surfaces on two sides of the switch element 90. Two pairs of positioning slots 93 at different levels are provided in conjunction with the guiding bevels 91 and 911. The top end of the retaining piece 80 projects over the combination seat 85 and the switch element 90 so that a shaft rod 94 may penetrate through the corresponding holes of the retaining piece 80 and two ends of the shaft rod 94 may be bracketed by the positioning slots 93.
Thus, a mounting seat 71, on which the CPU 73 and a heat sink 74 may be stacked, is disposed on a mainboard 70. Corresponding engaging blocks 72 on the external side of the mounting seat 71 engage with the retaining hole 81 of the retaining piece 80 and the retaining hole 76 of the retaining arm 75, respectively. Then, the switch element 90 is actuated to rotate relative to the combination seat 85 so that the switch element 90 is thus moved and the higher positioning slots 93 engage with the shaft rod 94. Thus, the shaft rod 94 and the retaining piece 80 are pulled up in a straight line direction so that the inner bottom edge of the retaining hole 81 of the retaining piece 80 tightly presses against the bottom side of the engaging block 72. Thus, the retaining arm 75 elastically presses against the heat sink 74 to retain the heat sink 74 in the mounting seat 71 and thus to attach the heat sink 74 to the CPU 73.
However, the shape of the switch element of the retaining device is quite complicated. For example, the guiding bevels with different levels and arced surfaces and two pairs of positioning slots with different levels cannot be easily formed on the circumferential side of the hollow body of the switch element. In addition, the machined shape of the combination seat is not simple because the combination seat has to be positioned to the retaining piece without rotation. Also, two sides of the top end of the retaining piece are not symmetrical. Thus, the cost has to be increased because many elements have complicated structures. The difficulty in the machining technology is increased and the stable quality cannot be ensured.